Electroplating nickel



United States Patent 1 2,881,120 ELECTROPLATING NICKEL Jack L. Towle, Cleveland, and James K. Long, Chesterland, Ohio No Drawing. Application August 26, 1957 Serial No. 680,415

8 Claims. (Cl. 204-49) This invention relates to the electrodeposition of nickel and more particularly is concerned with a process and solution for use in a process for the electroplating of nickel. The invention, more specifically, relates to the use of cooperating brightening agents in aqueous acid nickel plating solutions.

It has been discovered that excellent bright and smooth ductile deposits of nickel can be produced by electrolyzing an aqueous acid solution of a nickel electrolyte of the class consisting of nickel sulfate, nickel chloride, and mixtures of nickel sulfate and nickel chloride when such solutions also contain an effective amount of each of two cooperating addition agents. One of the cooperating addition agents is characterized in structure by a monoor di-ethylenically linked benzene nucleus and heterocyclic nitrogen-containing nucleus and is furthermore characterized as having a minimum solubility in the plating solutions of at least .01 gram per liter. Such compounds are hereinafter usually referred to as phenylalkylene substituted heterocyclic nitrogen containing compounds. The other cooperating addition agent is selected from the well known class of aromatic sulfonamides and aromatic sulfonates employable in modern acid nickel plating solutions as carriers or regulators for other brighteners. Such aromatic sulfonamides and aromatic sulfonates are cyclic organic sulfur compounds having a characteristic solubility in the plating solutions, such as of the Watts type, of at least 0.2 gram per liter and are furthermore characterised in containing the following group:

l The carbon atom in the group is a nuclear carbon atom of an aromatic nucleus such as a benzene or naphthalene ring and the balance of the remaining nuclear carbon atoms carry a group of the class consisting of hydrogen, methyl, ethyl, chlorine, CHO, phenyl, etc.

The phenylalkylene substituted heterocyclic nitrogencontaining compound may be employed in amounts ranging broadly from about .002 to about .2 gram per liter. Lesser amounts are usually' preferred when there is agitation of the plating solution as compared when no appreciable agitation is employed. The best ductility and brightness are usually obtained when the phenylalkylene substituted heterocyclic nitrogen-containing compounds are employed in amounts ranging from about .003 to about .1 gram per liter. Although the deposits obtained are usually very ductile as compared to most modern bright nickel deposits, they become more brittle when concentrations greater than about .2 gram per liter of the brightener are employed. The second additive, namely, additives selected from the groupconsisting of aromatic sulfonamides and sulfonates and mixtures thereof may be utilized in amounts ranging from about 0.2 to 20 grams per liter although preferably they are employed in amounts ranging from about 1 to 8 grams per liter.

2,881,120 Patented Apr. 7, 1959 The phenylalkylene substituted heterocyclic nitrogen compounds may be considered as having the following is a nitrogen-containing nucleus selected from the group consisting of pyridine, quinoline, and isoquinoline nuclei and wherein is a benzene nucleus. R is a monoor di ethylenic linkage, as for example, a vinylene or butadienylene group. This ethylenic type linkage between the benzene nucleus and a carbon of the nitrogen-containing nucleus is characteristic of the compounds according to the invention. R, is a substituent on a nuclear carbon atom of the nitrogencontaining nucleus and since there may be more than one R substituent, they are independently selected from a hydroxyl group, a chlorine group, an amine group, a nitro group, and alkyl and alkoxy groups having from 1 to 4 carbon atoms. x in the case of the formula may be an integer from 0 to 3. R like R is attached to a nuclear carbon atom only in this case R, is attached to a nuclear carbon atom of the benzene nucleus and is selected from a hydroxyl group, an amino group, a nitro group, and alkyl, alkoxy, alkylamino, and dialkylamino groups wherein the alkyl portions of the groups have from 1 to 3 carbon atoms. More than one R, substituent on the benzene nucleus may be tolerated and they are independently selected from the previously mentioned group, and m is an integer from 0 to 3. A is selected from alkyl and carboxyalkyl groups having from 1 to 4 carbon atoms. B is an anion of a water soluble acid and y and z are either both 0 to both 1. Both A and B are attached to the nitrogen atom.

Suitable phenylalkylene substituted heterocyclic nitrogen-containing compounds and their structural formulas are set forth in Table I. The optimum concentrations recommended are also set forth. Generally good deposits having good ductility will be obtained when utilizing the indicated compounds in their optimum quantities with a cooperating brightening agent of the aromatic sulfonamide or sulfonate type in acid plating solutions having a nickel electrolyte selected from nickel sulfate, nickel chloride and mixtures thereof.

TABLE I wherein grams/liter Z-styryl qulnollne N-ethyl, Myryl qutnoltnlnm etholulhto I 3 TABLE I-Continued grams/liter CHr-Cr OBOr-O 031GB: Htyryl qutnollne CH=CHO (I) N-ethyl, Htyryl gulnollnlum ethosullate CHI-C \OSO:O CHlCH: 2-(4'-dlmethylamlno styryl) quinollne N-ethyi, 2(4'-dlmethylamlno styryl) quinoltnlum ethosulfate omen-Omen, N

CHz-Cg OBOr-O CIIaCHI N-meth l, 2-(4'-phenyl butadlenyl-l' 3') qulnoiinlum perchlorate Ollnl cn-on-cm-cn-O C Cl N gboxymettul, l-ltml qutnollntum chlo- N H0 0 0-06, O 1 fl-(f-metboxy. f-hydmxyatyryl) qulnollna .oohom The second additive which cooperates with the ph yialkylene substituted heterocyclic nitrogen-containing compounds are those selected from the class of aromatic sulfonamides and sulfonates having solubility in the plating solution of at least .2 gram per liter. Thea'romatic sulfonamides and sulfonates are frequently called carriers or regulators in the trade and accordingly are so called herein in respect to their action with the phenylalkylene substituted heterocyclic nitrogen containing compounds. Sulfonamides are herein used in a sense to include sulfimides. Examples of aromatic sulfonamides which may be found useful as carriers are set forth in Table II and examples of aromatic sulfonates are set forth in Table III.

TABLE II (1) Benzene monosulfonamide CHSOQNH: (2) Saccharine, sodium salt C lfisO CONNa (3) p-Chlorobenzenesulfonamide CICHSCQNH: (4) Xylene sulfonamide (CH C H SO NH, (5) p-Toluenesult'onamide CH C H SO Nl-1, (6) Trichlorodibenzenesulfonamide Cl C,H SO,NHSO,C.H Cl (7) Tetrachlorodibenzenesulfonamide Cl,C l-l -,SO NHSO,C.H,Cl, (8) di-(fl-Naphthalenesulfonamide) CmHqSOgNHSOgCmHq (9) 2,2'4,4'6,6-hexachlorodihenzenesulfonamide Cl C H SO NHSO C,H,Cl, (10) Pentachlorodibenzencsulfonamide Cl C,H,SO,NHSO,C,H -,Cl, (ll) Methyldichlorodibenzcncsul fonamide CI C H SO NHSO QmCI-I (12) 2,4,6-trichlorodibenzenesulfonamide Cl C,H SO NHSO C,I-l (13) 2,5-dichloro-3'-sulfamyldibcnzenesulfonamide cl C l-l sO NHSO C H SO,NH, (14) Disulfonilamide NH,C,H S0,NHSO,C.H NH (15) N-phenylsulfonyl.fi-naphthalenesulfonamide C H SOWHSO C H', (16) di-n-Toluene sulfonamide CH C H SO,NHSO,C,H CH, (17) 4-methyldibenzenesulfonamide C H SO,NHSO C H CH,

(18) N,N'-bis(phenylsulfonyl -m-sulfamylbenzamide C l-1 SO,NHSO,C,H CONHSO,C H

(19) Dicumenesulfonamide (CH,) CHC H SO NHSO C H CH (CH,),

4-ethyldibenzenesulfonamide I C.H SO NHSO,C,H C,H, (21) 4,4'-dicarboxyldihenzenesulfonamide COOHC,H SO,NHSO,C H COOH (22) 2,2',4,4'-tetramethyldibenzenesulfonamide s 2 e a 2 a e a( C 1):

5 (30) ,p'-Methylene-bis-(dibenzenesulfonamide) C l-1 80MHSO,C H.,CH C H,SO NHSO C H (31) N,N-bis-(2,4,6-trichlorophenylsulfonyl) 1,3-benzenedisulfonamide Cl C H SO NHSO C H SO NHSO,C H Cl (32) N,N'-bis-(p-tolylsulfonyl)- 4,4'-diphenyldisulfonamide CH C H SO NHSO C H C H SO NllsO C l-l Cl-i (33) N-ethylsulfonylbenzenesulfonamide C H SO NHSO CH CH (34) N-vinylsulfonylbenzenesulfonamide c rnso ruiso cn=(3H (35) N-(butylsulfonyl benzenesulfonamide C H SO NHSO C H (36) N- (n-laurylsulfonyl -benzenesulfonamide C H SO NHSO C l-l (37) di-a-Toluenesulfonamide C H CH SO NHSO CH C H (38) N-benzylsulfonylbenzenesulfonamide C H SO NHSO CH C I-i (39) N-ethylsulfonyldichlorobenzcnesulfonamide ouch-[ 50 Muso c u (40) N-methallylsulfonylbenzencsulfonamide C H SO NHSO CH C(CH =CH (41) N-methylsulfonylbenzenesulfonamide C H SO NHSO CH (42) N,N'-bis- (phenylsulfonyl) -1,5-naphthalenedisulfonamide C H SO NHSO C H SO NHSO C H N,N'-bis(phenylsulfonyl) 3,3 '-benzophenonedisulfonamide C H S0 NHSO C H COC l-l SO NHS0 C l-l (44) Bi-(dibcnzenesulfonamide) C H SO NHSO C H C H SO NHSO,C H

TABLE III (i) Benzene monosulfonic acid C H SO H (2) Benzenedisulfonic acid s A a M (3) Sodium benzene monosulfonate C5H5SO3N3. (4) Nickel benzene monosulfonate I s 5- a)2 (5) Monochlorobenzene monosulfonic acid ClC H SO H (6) Dichlorobenzene disulfonic acid 2 0 z( a )a (7) 2,5-dibromobenzene sulfonic acid Br C H SQ H (8) Toluene sulfonic acid CH C H SO H (9) Benzaldehyde sulfonic acid C H (CHO)SO H (10) Diphenylsulfonic acid C H C H SO H (ll) Benzene sulfonyl chloride C H SO Cl (12) Thiophene sulfonic acid C4H3S'SO3H (13) Diphenyl sulfone c n so c u (14) Naphthalene disulfonic acid C1OH6(SO3H)2 (15) 1,3,6-naphthalene trisulfonic acid 1o s( s )s From the aromatic sulfonamides and sulfonates set forth respectively in Tables ll and lil, it is clear that numerous ring compounds containing the effective ro p mav be used. Aromatic cnmnmmris such a: the

benzene sulfonic acids or heterocyclic compounds with aromatic characteristics such as thiophene sulfonic acid may be used as carriers. Various substituents on the ring structures are also exemplified. The carrying agents or regulators produce a degree of brightness without any brightencr, but not enough to yield full brightness alone.

The constituents of the plating bath according to the preferred practice of the invention are (1) water, (2) nickel, sulfate, nickel chloride or nickel sulfate and nickel chloride, (3) an aromatic sulfonate or an aromatic sulfonamide or mixtures or a plurality thereof, (4) a wetting agent (optional), and (5) a phenylalkylene substi -tuted heterocyclic nitrogen compound of the type set forth in the foregoing structural formula or mixtures of such compounds. An additional ingredient of the solution which is desirable is a buffering agent such as boric acid, formic acid, ammonium sulfate, or the like.

It will be noted that in respect to major constituents of the nickel plating solution, these solutions are similar to the well known all sulfate, all chloride, and sulfate chloride or Watts type" acid nickel plating solutions. The essential novel feature of the invention is the use of acid nickel plating solutions having one or more nickel electrolytes selected from nickel sulfate and nickel chloride and additionally containing at least one aromatic sulfonamide and/or sulfonate and a small amount of at least one aralkylene substituted heterocyclic nitrogencontaining compound of the class heretofore set forth.

The basic solutions in connection with which the re- Wetting agent (e.g. sodium lauryl sulfate) 0 to 0.5 gram, preferably H O to make 1000 cc. 0.05 to 0.2 gram.

All chloride NiCl,-6H O so to 250 grams, preferably to 200 grams. Boric acid 0 to 60 grams, preferably Wetting agent (e.g. sodium 10 to 40 grams.

lauryl sulfate) 0 to 0.5 gram, preferably H 0 to make 1000 cc. 0.05 to .2 gram.

Sulfate-chloride watts type NiSO,-7H O 100 to 400 grams, prefer- NiCl -6H O ably 200 to 300 grams. Boric acid 10 to 60 grams, preferably Wetting agent (e.g. sodium 25 to 40 grams.

lauryl sulfate) 0 to 50 grams, preferably 15 to 40 grams.

H O to make 1000 cc. 0 to 0.5 gram, preferably 0.025 to 0.2 gram.

The plating solutions above identified may be operated under conditions of pH, temperature and current density which are customarily employed and bright ductile deposits will be obtained. Preferred operating conditions for the typical basic solutions are as follows:

All All Watts Sulfate Chlorlde pll 3. 5 3 3. 5 Temperature, F 140 gen-containing type compound described above. The solution should. for best results, contain an anti-pit agent, although the deposits may be suitable for some purposes without eliminating the pitting, and under some conditions wherein the deposits may not be objectionably pitted even in the '5 absence of an addition agent for controlling of pitting. 13 fl t f g eterocvcllc nucleus selected Sodium lauryl sulfate or other alkyl sulfates having 8 m E grouilconslsunl of pyndmc' qumohm" to 18 carbon atoms may-be used as an anti-pit agent, qumolm nude, although its use is not essential and other wetting agents or mixtures of wetting agents may be used for control Q of pitting. Sodium octyl sulfate is an excellent wetting agent when agitation is employed. is a benzene nucleus, R is a divalent radical selected The invention is best illustrated by the examples set from the group consisting of vinylene and butaforth in Tables IV and V. Table IV sets forth solutions dienylene radicals and connected to a carbon atom of the containing the principal basic constituents whereas Table nitrogen containing nucleus and to a carbon atom of the Vsets forth the cooperating brighteners employed. Table benzene nucleus, R is a substituent on a carbon atom V also sets forth the plating conditions utilized in the of the nitrogen containing nucleus selected from the respective solutions of Table IV. group consisting of hydroxyl, chlorine, amino, nitro, TABLE Iv alkyl having from 1 to 4 carbon atoms and alkoxy haw 0 ing from 1 to 4 carbon atoms, x is an integer from 0 to 3, R, is a substituent on a nuclear carbon atom of the a benzene nucleus selected from the group consisting of hydroxyl, amino. nitro, alkyl having from 1 to 3 carbon 250 atoms, alkoxy having from 1 to 3 carbon atoms, alkyl 40 40 5 amino having from I to 3 carbon atoms, and dialkyl ;5}f,,,;;,;, sumo n 2 t? amino having from 1 to 3 carbon atoms, m is an integer e s to1 0 from 0 to 3, A is a substituent on the nitrogen atom of the nitrogen containing nucleus selected from the group TABLE V ExpcrlmentNo 1 214567801011 I213 tats 171519m2l22flfll Solutlnncmployed .ABAABAABAAAABBBAAUAAABBBB 1st Addition agent (sce cnrres.

N0. Table l.)

AANWNW s ucepan" gnooqmvmsure ll (g./l.l Bl(dlbcnzcnc sulfonnmldo) Sacchnrln. Sodlum Sult.. Naphthalcne disullflnltacld l,;i{.t -naphthalcne trlsultonlc acld.

iarrtpcrature, F I10 Current density (Amps/H3)..." 40 Agltutlon 1 Sec Table IV. I Nono.

Air.

We claim:

1. The process for electroplating bright ductile nickel deposits comprising electrolyzing an acid nickel electrolyte containing aqueous solution between an anode and cathode wherein said solution contains at least one nickel compound from the group consisting of nickel chloride and nickel sulfate, said solution further containing cooperating brightening agents, one of said cooperating brightening agents being selected from the group consisting of aromatic sulfonamides and aromatic sulfonates and mixtures thereof having a solubility in said solution of at least 2 gram per liter, and another of said cooperating brightening agents being selected from the group consisting of compounds and mixtures thereof having a solubility in said solution of at least .01 gram per liter and characterized by the following formula:

consisting of alkyl and carboxyalkyl having from 1 to 4 carbon atoms, y is an integer from 0 to l, B is an anion of a water soluble acid attached to the nitrogen atom of the nitrogen containing nucleus, z is an integer from 0 to 1 and z is 1 when y is 1, said first mentioned brightening agent being present in said solution to the extent of from 0.2 to 20 grams per liter and said second mentioned brightening agent being present in said solution to the extent of from 0.002 to 0.2 gram per liter.

2. The process according to claim 1 wherein said first mentioned cooperating brightening agent is contained in said solution in amounts ranging from 1 to about 8 grams per liter and said second mentioned cooperating brightening agent is contained in said solution in amounts ranging from about .003 to about .1 gram per liter.

3. The process according to claim 1 wherein said first mentioned brightening agent is selected from the class consisting of bi(dibenzenesulfonamide), saccharin, and naphthalene sulfonic acids, and wherein said second mentioned cooperating brightening agent is selected from the group consisting of N-methyl,4-(4'-phenylbutadienyll,3')quinolinium perchlorate; N-methyl, 2-(4'phenylbutadienyl-l',3)quinolinium perchlorate; N-methyl, 2- (4'-phenylbutadienyl-l',3)quinolinium perchlorate; 2 styryl quinoline; 4-styryl quinoline and N-carboxymethyl, 4-styryl quinolinium chloride.

4. The process according to claim 3 wherein said first mentioned cooperating brightening agent is contained in said solution in amounts ranging from about 1 to about 8 grams per liter and said second mentioned cooperating brightening agent is contained in said solution in amounts ranging from about .003 to about .1 gram per liter.

5. A nickel electroplating solution comprising at least one nickel compound selected from the group consisting of nickel chloride and nickel sulfate, 9. cooperating brightening agent selected from the group consisting of aromatic sulfonamides, aromatic sulfates and mixtures thereof having a solubility in said solution of at least .2 gram per liter, and another cooperating brightening agent selected from the group consisting of compounds and mixtures thereof having a solubility in said solution of at least .01 gram per liter and characterized by the following formula:

(Ms (B)- is a nitrogen containing heterocyclic nucleus selected from the group consisting of pyridine, quinoline and isoquinoline nuclei,

wherein 10 stituent on a nuclear carbon atom of the benzene nucleus selected from the group consisting of hydroxyl, amino. nitro, alkyl having from 1 to 3 carbon atoms, alkoxy having from 1 to 3 carbon atoms, alkyl amino having from 1 to 3 carbon atoms, and dialkyl amino having from 1 to 3 carbon atoms, m is an integer from 0 to 3, A is a substituent on the nitrogen atom of the nitrogen containing nucleus selected from the group consisting of alkyl and carboxyalkyl having from 1 to 4 carbon atoms, y is an integer from 0 to 1, B is an anion of a water soluble acid attached to the nitrogen atom of the nitrogen containing nucleus, z is an integer from 0 to l and z is 1 when y is 1, said first mentioned brightening agent being present in said solution to the extent of from 0.2 to 20 grams per liter and said second mentioned brightening agent being present in said solution to the extent of from' 0.002 to 2.0 grams per liter.

6. A nickel plating solution according to claim 5 wherein said first mentioned cooperating brightening agent is contained in said solution in amounts ranging from 1 to about 8 grams per liter and said second mentioned cooperating brightening agent is contained in said solution in amounts ranging from about .003 to about .1 gram per liter.

7. A nickel plating solution according to claim 5 wherein said first mentioned cooperating brightening agent is selected from the group consisting of bi(dibenzenesulfonamide), saccharin, and naphthalene sulfonic acids, and said second mentioned brightening agent is selected from the group consisting of N-methyl, 4-(4'- phenylbutadienyl l,3')quinolinium perchlorate; N methyl,2 (4' phenylbutadienyl l,3')quinolinium perchlorate; 2-styrylquinoline; 4-styryl quinoline, and N- carboxymethyl, 4-styryl quinolinium chloride.

8. A nickel plating solution according to claim 7 "wherein said first mentioned cooperating brightening agent is contained in said solution in amounts ranging from about 1 to about 8 grams per liter and said second mentioned cooperating brightening agent is contained in said solution in amounts ranging from about .003 to about .1 gram per liter.

References Cited in the tile of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,881,120 April 7, 1959 Jack L. Towleet a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, lines 1 and 2, for Jack L. Towle, of Cleveland, and James K. Long, of Chesterland, Ohio, read Jack L. Towle, of Cleveland, and James K. Long, of Chesterland, Ohio, assignors to The Harshaw Chemical Company, of Cleveland, Ohio, a corporation of Ohio,; line 11, for Jack L. Towle and James K. Long, their heirs read -The Harshaw Chemical Compan its successors; in the heading to the printed specification, lines 3 and 4, for Jack L. Towle, Cleveland, and James K. Long, Chesterland, Ohio read -Jack L. Towle, Cleveland, and James K. Long, Chesterland, Ohio, assiinors to the Harshaw Chemical Company, Cleveland, Ohio, a corporation of Ohio; in t e printed specification, column 2, line 43, for 0 to both 1 read 0 or both 1-; same column 2,1me 55, through column 3, line 75, Table I should appear as shown below instead of as in the patent TABLE I grams/liter 1 2-styryl qulnoline 003-. 02

2 N-ethyl, 2-styry1 qulnolinlum ethosulfate 003-. 02

CHg-Cg OBO -OCILCH;

3 4-styry1 qulnoline 003-. 02

CH=CH O? 4 N-ethyl, 4-styryl quinolinium ethosulfate 003-. 02

CINE- 3 3 CHz-CH: OSOr-OCHgCH 5 2-(44Limethylamino styryl) qulnoline 01-. 1

a N-ethyl 2 (4'-dimethylamino styryl) quin- .01-.04

oliniurh ethosulfate 7 N-methyl 2-(4-phenyl butadienyl-l, 3) ,004-,01

quinulinlum perchlorate (Ilerecn-omoH-Q TABLE I-Contlnued grams/liter 8 N-methyl, 4-(4-pbenylbutndienyI-1',3) quln- .004-.007

ollnium perchlorate c11=cmcrr=czr 9 Nfiarboxymethyl, 4-styryl quinollnium chlo- .0O25-.007

HO C--O 1 01 2-(3'-methoxy, 4'-hydroxystyryl) quinollne .0031 008 column 5, line 13, for N -(b'utylsulfonyl)benzenesulfonamide" read -(35) N- (nbutylsulfonyl)benzenesu1f0namide; column 6, line as shown below instead of as in the patent- All sulfate NiSO -7H 0 100 to 400 grams, preferably 200 to 300 grams. Boric acid 0 to 60 grams, preferably 10 to 40 grams. Wetting agent (e.g. sodium lauryl sulfate) 0 to 0.5 gram, preferably 0.05 to 0.2 gram. H 0 to rna.ke..w ....v 1000 cc.

All chlwi-J'e NiCl -6H O to 250 grams, preferably 100 to 200 grams. Boric acid 0 to grams, preferably 10 to 40 grams. Wetting agent (e.g. sodium lauryl sulfate) w 0 to 0.5 gram, preferably 0.05 .i0 .2 gram. H O to make 1000 cc.

Sulfate-chloride Watts type NiSO -7H O to 400 grams, preferably 200 to 300 grams. NiCI 61-1 0 10 to 60 grams, preferably 25 to 40 grams. Boric acid 0 to 50 grams, preferably 15 to 40 grams.

Wetting agent (e.g. sodium lauryl sulfate) 0 to 0.5 gram, preferably 0.025 to 0.2 gram. H O to make 1000 es.

s 31 two 57, inclusive, should appear column 7, Table V, No. l (g./1.), insert a decimal point before the first three items; same table, N0. 5 (g./1.), under 12A, for 05 read -.O5; column 8, line 66, after from insert about column 9, lines 2 and 3, strike out N -methyl, 2- (4'- heny1- butgdienyl-l'fi')quinolinium perch10rate; column 10, line 21, after from insert a. oub.

Signed and sealed this 1st day of September 1959.

[SEAL] Attest:

KARL H. AXLINE, ROBERT C. WATSON, Attesting Ofiioer. Commissioner of Patents. 

1. THE PROCESS FOR ELECTROPLATING BRIGHT DUCILE NICKEL DEPOSITS COMPRISING ELECTROLYZING AN ACID NICKEL ELECTROLYTE CONTAINING AQUEOUS SOLUTION BETWEEN AN ANODE AND CATHODE WHEREIN SAID SOLUTION CONTAINS AT LEAST ONE NICKEL COMPOUND FROM THE GROUP CONSISTING OF NICKEL CHLORIDE AND NICKEL SULFATE, SAID SOLUTION FURTHER CONTAINING COOPERATING BRIGHTENING AGENTS, ONE OF SAID COOPERATING BRIGHTENING AGENTS BEING SELECTED FROM THE GROUP CONSISTING OF AROMATIC SULFONAMIDES AND AROMATIC SULFONATES AND MIXTURES THEREOF HAVING A SOLUBILITY IN SAID SOLUTION OF AT LEAST 2 GRAM PER LITER, AND ANOTHER OF SAID COOPERATING BRIGHTENING AGENTS BEING SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS AND MIXTURES THEREOF HAVING A SOLUBILITY IN SAID SOLUTION OF AT LEAST 01 GRAM PER LITER AND CHARACTERIZED BY THE FOLLOWING FORMULA: 